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Multispecies Stock-Assessment Modeling (MSM) is a three-species model of some of the most productive fish stocks and key predators in the Bering Sea – walleye pollock, Pacific cod, and arrowtooth flounder. Their biological interactions may influence natural mortality estimates and subsequent harvest recommendations. Thus MSM is a first-cut approach for implementing ecosystem-based management of fisheries resources in the Bering Sea.

Because MSM can capture critical threshold effects that characterize many ecological interactions, such an approach also provides a statistical framework to evaluate and manage both the direct and indirect effects of fisheries harvest on multiple species. Additionally, we used projections of the model to derive biological reference points (BRPs) for various harvest control rule approaches under variable climatic conditions.

As part of the MSM modeling effort we have continued to update the bioenergetic parameters used in MSM. In particular, we recently completed a comparative analysis of field-based daily ration values (corrected for digestion) to bioenergetic-based ration estimates for the eastern Bering Sea (EBS), Gulf of Alaska (GOA), and Aleutian Islands (AI) regions for walleye pollock, Pacific cod, and arrowtooth flounder.

For this we refit Wisconsin bioenergetic parameters to published consumption data for the three (or similar) species and compared bioenergetic rations to digestion corrected field-based ration estimates (using two different methods) and von Bertalanffy derived estimates of consumption (Fig. 1). This allowed us to derive consumption parameters that can now be used to update regional MSM models.

Additionally we have conducted a detailed analysis of allometric patterns in predation risk and prey selectivity (Fig. 2). These analyses have allowed us to parameterize the size-based foraging model used in MSM.

We have applied the updated bioenergetic and foraging model parameters to the MSM model for the EBS. In particular, we have generated projections for the three species under various target harvest rates including (i) no fishing, and (ii) fishing to 40% of the unfished spawning biomass. Model predictions were compared to single species assessments from 2011 as well as Ecosim predictions for the Bering sea (Fig. 3).

We now are in the processes of generalizing the MSM model code to accommodate additional species, initially anticipated to include Steller sea lions and Bering Sea flatfish species.

The updated model and initial model results are being compiled in a draft manuscript titled "Incorporating bioenergetics into multi-species statistical catch-at-age models: an example from the Bering Sea."